PROJECT SUMMARY/ABSTRACT Esophageal adenocarcinoma (EAC) is a serious clinical problem due to its rapidly increasing incidence rate, and the limited treatment options currently available. This disease has now overtaken other histological types of esophageal tumors in the US. The major risk factor for EAC is gastroesophageal reflux disease (GERD), which affects 10 to 20% of the US population. Under conditions of GERD, esophageal cells are ex- posed to acidic gastric juice mixed with duodenal bile salts. The reflux exposure causes chronic inflammation, and excessive oxidative DNA damage, resulting in the accumulation of tumorigenic alterations and progression to EAC through Barrett's metaplasia (BE). However, the precise molecular events underlying the malignant transformation of esophageal cells remain poorly understood, thereby limiting the identification of targets for screening at risk patients and the development of new therapies for esophageal tumors. We have developed an innovative hypothesis to investigate tumorigenic transformation of esophageal cells in conditions of esophageal reflux injury. This hypothesis is supported by strong preliminary data from human tissues, animal models, and extensive in vitro studies. We have demonstrated that the 6Np73 protein plays a critical role in esophageal tumorigenesis by inhibiting key tumor suppressor proteins in Barrett's esophageal cells exposed to chronic gastroesophageal reflux. We have also identified pathological factors that lead to 6Np73 activation. We will build on these findings to further investigate the role played by 6Np73 and other members of the p53 protein family in the progression to esophageal adenocarcinoma. In aim 1, we will dissect the mechanisms of 6Np73 upregulation during progression to EAC. In aim 2, we will investigate esophageal tumorigenesis in vivo. We will employ novel mouse model of gastroesophageal reflux injury and esophageal organotypic cul- tures to recapitulate human GERD-associated pathology and dissect the function of 6Np73. These studies will be complemented with analyses of human esophageal precancerous and cancerous lesions. In aim 3, we will explore the biological functions in the regulation of oxidative DNA damage induced by gastroesophageal reflux. Our findings will have a strong impact on the understanding of multistep tumorigenesis associated with GERD and BE. Importantly, our results could help to reveal potential risk factors for esophageal tumor devel- opment and lay the groundwork for development of novel chemotherapeutic approaches in at risk patients with GERDand BE.